Reference is made to abandoned application Ser. No. 944,729--Anthony et al, filed Dec. 22, 1986, assigned to the same assignee as the present invention, which discloses an improved method and apparatus by which diamond crystals are caused to nucleate and grow on a preferred substrate by means of a heated filament and luminescent gas plasma activated hydrogen-hydrocarbon gas mixture coming into contact with the substrate. The copending application discloses that a hydrogen-hydrocarbon gas mixture subjected to concurrent activation by an incandescent tungsten wire electrical resistance heater and by electromagnetic microwave energy becomes a luminescent gas plasma with a significant atomic hydrogen content. The activated gas mixture is brought into contact with a heated substrate, and as a consequence thereof, diamond crystals are formed or nucleated on the substrate from the gas mixture with subsequent diamond crystal growth. The noted process is referred to as a chemical vapor deposition, CVD, process. From the copending application, it is also known that diamonds may be obtained from the described CVD process without the use of microwave energy, as shown in U.S. Pat. No. 4,434,188 which described a CVD process of causing diamond nucleation and growth from a heated gas mixture in contact with a substrate.
In general, the CVD process involves selection of operating parameters such as selection of a precursor gas and diluent gases, the mixture proportions of the gases, gas temperature and pressure, the substrate temperature and means of gas activation. When these parameters are adjusted to provide diamond nucleation and growth on a substrate, there is, as an unavoidable consequence of the process, codeposition of graphite on the substrate along with the diamond. When the parameters are adjusted to provide for removal of the graphite by gasification or minimal deposition or graphite, diamond nucleation and growth significantly decrease. The known CVD processes for producing diamond crystals can be described as continuous processes which attempt to establish those conditions of pressure, temperature, and gas mixture which provide an acceptable rate of diamond crystal nucleation and growth, and only minimal graphite codeposition.
In order to grow diamond crystals at a reasonably high rate in the CVD process as described, the operating parameters are usually set as a compromise between deposition of graphite and diamond crystal growth, or between diamond growth and graphite removal. Ordinarily, such a compromise may be acceptable where the operating parameters can be set to establish conditions under which graphite codeposition is restrained and some diamond crystal growth continues, but means are needed to achieve graphite removal in a shorter time period, e.g., providing maximum short term clean up without overall reduction of high rate diamond growth.